JP2000061816A - Polishing pressure modulating cmp device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To flatten a semi-conductor wafer and other work piece by periodically applying the downward or upward force to any one of a wafer pushed to a polishing pad or the polishing pad during the flattening. SOLUTION: Downward or upward force is periodically applied to a wafer or a pad 13. In the case where the force is applied to the pad 13 and the periodical force is interrelated with the relaxing time of the pad, a chemical and mechanical flattening process is remarkably improved. During the operation of the chemical and mechanical flattening process in the normal condition, the periodical force and the compressibility of the pad 13 are interrelated with each other so that a height of the pad 13 is maintained between a compression height 13b expressed with dotted lines 13d, 13e and a compression released height 13c. Height of the pad 13 between the dotted lines 13d, 13e is defined as Hop. Height of the pad 13 is higher than the compression height 13b, and lower than the compression released height 13c. Chemical and mechanical flattening process is remarkably improved by operating this process within a range Hop of the operation height of the pad 13, and an improved result of flattening can be obtained.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the processing of semiconductor wafers, such as slices of semiconductor silicon in the fabrication of electronic components, and more particularly to wafers in a chemical mechanical planarization process to achieve a high degree of wafer planarity. An improved method and apparatus for planarizing a substrate.

[0002]

BACKGROUND OF THE INVENTION In the manufacture of electronic components such as integrated circuits, wafer surface planarity is extremely important. Photolithography processes are generally pushed close to the limit of resolution so that the electromagnetic or other radiation used to create integrated circuits can be accurately focused to a single level, and thus the surface of the wafer. It is essential that the wafer surface be highly flat so that accurate imaging can be achieved throughout. Wavy, curved, or wedge-shaped semiconductor disks result in a lack of definition, for example, when a photosensitive resist is applied to the surface of the disk and exposed.

Currently in the industry, chemical mechanical planarization processes are commonly used to achieve the flatness required to fabricate ultra-high density integrated circuits and other electronic component circuits. Generally, a chemical mechanical planarization (CMP) process presses a semiconductor wafer against a moving polishing surface that has been wetted with a chemically reactive polishing slurry.
Slurries are usually basic or acidic and generally contain alumina or silica particles. The planarized surface is usually a relatively soft, flat pad made of a porous material such as polyurethane foam. The pads are typically mounted on a flat rotating platen, although linear transfer pads as described below have also been proposed.

Generally, the wafer is fixed to a carrier plate (or wafer carrier) by an attachment medium such as an adhesive, and the wafer is rotated or linearly moved by being loaded with a force applied through the carrier by a pressure plate. Frictional contact with a flattening pad mounted on the table. The carrier and the pressure plate are also rotated by drive friction from the rotary turntable or from rotary drive means mounted directly on the pressure plate for the rotary turntable or linear turntable or linear transfer pad.

In a typical planarization machine, the movement of a carrier takes a wafer from a first station, conveys the wafer to a planarization surface, drives the wafer across a rotating planarization surface, From the planarization surface to the second station and programmed to release the wafer at the second station. A common method of securing and releasing a wafer is to use a vacuum head that includes a rigid perforated plate against which the wafer is attracted by applying a vacuum to the space above the perforated plate.

During planarization, when force is applied to the wafer, especially when using a rotating pad and turntable, the planarizing action across the wafer is not uniform, resulting in a non-uniform thickness from center to edge. It has been found that the flatness is not sufficient. The surface life of the planarization pad is also a factor affecting the flatness of the planarized wafer. The frictional heat generated at the wafer surface enhances the chemistry of the planarizing fluid, thus increasing the planarization rate. But,
Friction heat can cause planarity problems if the heat is not transferred evenly over the wafer surface, and typical planarization systems utilize cooling systems to control the temperature of the planarization operation. ing.

In the prior art, many attempts have been made to improve the planarity of CMP operations. In U.S. Pat. No. 5,270,316, non-uniform pressure transmission, which causes different degrees of wear of the flattened disc, results in a soft elasticity between the pressure piston and the back of the carrier plate on which the flattened disc is fixed. By placing the insert, it is compensated. U.S. Pat. No. 4,313,284
In US Pat. No. 6,037,027, a deformable thin disk carrier is attached to a rotating pressure plate via an elastic device, whereby the carrier is deformed into a concave or convex shape depending on the required planarization. In U.S. Pat. No. 4,910,155, a dam is provided on the planarizing plate to completely submerge the planarizing pad in the planarizing pool of slurry. U.S. Pat. No. 4,918,886
In No. 9, compressed air acting on the pressure plate is used, and the pressure on the wafer surface can be made uniform. In US Pat. No. 5,036,630, a wafer carrier includes at least two materials having different coefficients of thermal expansion that provide the desired concave or convex bias to the wafer during a planarization operation. In U.S. Pat. No. 5,423,716, the underside of the backing plate of the wafer carrier includes a number of recessed areas against which a vacuum can be selectively applied. When a vacuum is applied, the elastic membrane is drawn into the recessed area, pulling the wafer into place. The same device can be used to apply a pressurized fluid to the wafer to exert a uniform downward pressure on the wafer. US Patent No. 548612
In No. 9, the wafer carrier pressure head comprises several pressure applicators above the wafer surface, which can be adjusted to monitor and vary the pressure exerted on the wafer during the planarization operation.

In US Pat. No. 5,486,265, uniform chemical-mechanical planarization can be achieved with high material removal rates by pulsing the pressure on the planarized wafer. The pressure is pulsed between an initial optimum pressure and a second, lower pressure, preferably about 0 psi, so that the cleaning slurry reaches all parts of the wafer surface and lacks a sufficient amount of cleaning slurry. Try to eliminate the negative effects of.

In US Pat. No. 5,522,965, a non-rotating planarizing pad is used to apply energy, eg, ultrasonic energy, to the pad to help remove surface material from the wafer and condition the pad. There is disclosed a method of conversion.

The disclosures of the above patents are incorporated by reference.

The CMP process described above, which is basically referred to as the rotary or orbital polishing technique, was primarily directed to methods commonly used in the industry today. The limitations of such spinning or orbiting techniques are becoming increasingly apparent as wafers are inherently exposed to unequal radial velocities on their surface during polishing. The removal rates vary across the wafer surface due to their increasing velocity along the radius of the polishing platen and pad.

The next generation CMP process will be a non-rotational technique referred to herein as the linear planarization technique (LPT). This technique uses a linear belt polishing pad to eliminate the unequal radial velocities encountered during rotary or orbital polishing. Such technology is described in "Linear" published by OnTrak Systems, Inc.
It is shown in a paper entitled "Planarization Technology". LAM Research also announced "Teres ^TM CMP Sy" dated February 1998.
This technique is described in a paper entitled "Stem Linear Planarization Technology (LPT)". In the LPT and rotary (orbital) techniques, the polishing pressure is applied from below the polishing pad via a fluid flow (air or water) or above the polishing pad as is commonly used in rotary or orbital processes. .

For convenience, the following description is directed to a rotary CMP process and a process in which polishing pressure is applied to the wafer from above the pad, but the method and apparatus of the present invention will be described in other CM.
Those skilled in the art will understand that it can also be used for the P process.

[0014]

With the problems and drawbacks of the prior art in mind, therefore, one object of the present invention is to provide an improved apparatus for planarizing semiconductor wafers and other workpieces, such as A CMP apparatus is provided.

Another object of the present invention is to provide an improved method of planarizing a workpiece, such as a wafer, using a planarizing apparatus such as a CMP apparatus.

Another object of the present invention is to provide a planar workpiece containing a planarized semiconductor wafer made using the improved method and apparatus of the present invention.

Other objects and advantages of the present invention will be readily apparent from the following description.

[0018]

The above and other objects apparent to those skilled in the art are achieved by the present invention. The present invention, in a first aspect, applies a periodic downward or upward force to either the wafer or the pad pressed against the polishing pad during planarization, and the height of the pad relative to conventional conventional planar surfaces. Pad compressibility to maintain a cyclic force between the compressed and decompressed positions as is commonly used in the compression process.
A method for planarizing a workpiece, such as a semiconductor wafer, in a chemical mechanical planarization process, including correlating with.

In another aspect of the present invention, there is provided a chemical mechanical planarization apparatus having a rotary turntable or a linear movement platen and a compressible planarization pad having a relaxation time (unit: second) on its surface of TR. The step of applying a planarizing slurry to the surface of the pad, the step of providing the substrate to be planarized, and the periodic downward facing of the substrate or polishing pad to maintain the substrate against the surface of the pad. And providing an upward force,
The height of the pad is maintained during the action of the force between the compressed height and the decompressed height according to the equation: TR> THI and TLO (where THI is the force of the pad in the downward direction). And TLO is the time when the pad is subjected to an upward force) continuing the method until the substrate is planarized. To do.

In a further aspect of the invention, a rotatable turntable or linear translation platen assembly,
A compressible planarizing pad supported on the assembly and having a relaxation time (in seconds) TR and located above the assembly and fixed on the lower surface of the carrier and disposed between the carrier and the planarizing pad. While flattening the workpiece,
A rotating carrier adapted to hold and a periodic downwards and upwards on the carrier and workpiece or on the pad to maintain the height of the pad between the compressed and decompressed positions during the planarization process. An apparatus for planarizing a surface on a workpiece, such as a semiconductor wafer, comprising means for providing a force.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In describing the preferred embodiment of the present invention, reference will be made to FIGS. In the figures, like numbers refer to like features of the invention. Features of the invention are not necessarily shown to scale in the drawings.

Referring to the drawings, FIG. 4 shows a prior art rotary CMP apparatus for planarizing a semiconductor wafer. A planarizing device, generally designated 10, can be used in the method of the present invention and includes a planarizing wheel assembly, generally designated 11. The flattening wheel assembly includes a flattening table or platen 12 having a compressible flattening pad 13 attached thereto. The flattening table 12 is a suitable motor or drive means (not shown).
Causes the shaft 14 to rotate in the direction indicated by the arrow 15. The planarizing pad is typically a compressible polyurethane of about 56 cm (about 22 inches) in diameter and about 0.13 mm (about 0.050 inches) in thickness.

A wafer carrier, generally designated 17,
The assembly is a wafer holding wafer 16 as shown.
A carrier 18 is included. A pressure plate 19 is provided on the wafer carrier 18 for applying force to the wafer carrier and the wafer.
Fixed to. In the illustrated embodiment, the hollow spindle 20
Is coupled to a pressure plate and is driven by a suitable motor or drive means (not shown) to move the wafer carrier assembly 17 in the directions indicated by arrows 21, 22 and 23. Spindle 2 as shown by arrow 31
0 can be loaded by pressure, or by using a pressurized fluid, such as compressed air, to feed it into the space 24 of the wafer carrier assembly to press the upper surface of the wafer carrier 18. be able to. The force is substantially uniform on the surface of the wafer carrier and the wafer.

During planarization, the slurry (not shown) is pad 1
Wafer carrier assembly 1 coated on surface 3
Flow between a wafer 16 supported by 7 and the planarizing pad 13 of the planarizing wheel assembly 11. The force exerted on the wafer carrier 17 and its rotation and movement on the surface of the planarization wheel assembly planarizes the side of the wafer 16 in contact with the planarization pad 13. As discussed above, flattened wafers are usually non-planar due to many factors, such as overheating, excessive amount of slurry in certain parts of the wafer, and different speeds of rotation in different parts of the wafer. Thus, it has one or more of the following features. That is, the outer edge of the wafer is thick, the load in the chip is uniform, the uniformity over the entire wafer is insufficient, and the planarization speeds of the wafers do not match.

As is well known in the art, multiple wafers and / or multiple wafer carriers can be simultaneously processed on a single planarization turntable during a planarization operation.

FIG. 5 shows a linear pad CMP apparatus for planarizing a semiconductor wafer. The pad 13 is a rotating member 32.
Platen 1 moved in the direction of the arrow by a and 32b
Move linearly on 2. Similar to wafer carrier assembly 17 shown in FIG. 4, wafer carrier assembly 17 is in a downwardly moving position in the direction of arrow 31 in the figure for contacting linear pad transfer surface 13. The wafer carrier assembly comprises a spindle 20 coupled to a pressure plate 19, preferably by a suitable motor or drive means (not shown) for moving the wafer carrier assembly in the direction indicated by arrow 23. Driven. The wafer 16 is supported by the pressure plate 19,
As the wafer carrier assembly moves in the direction of arrow 31, it contacts the surface of linear transfer pad 13.

The present invention is notable for planarization of wafers using a chemical mechanical planarization process when periodic forces with vertical upward and downward directions are exerted on the wafer or polishing pad and thus on the pad. It is based on the finding that the cycle time of the periodic force or the cycle time correlates with the compressibility of the pad. Broadly speaking, the process is such that during steady state operation of the planarization process, the pad height is maintained between the compression height and decompression height as achieved using prior art CMP processes. As such, applying a periodic force to the wafer or pad, and thus to the pad, and using a pad having a defined compressibility. Therefore, it is important to correlate the periodic upward and downward forces on the wafer and pad with the compressibility of the pad, which determines the relaxation time (TR) of the pad.
The relaxation time (TR) of a pad can be defined as the time it takes for a compressed pad to return to its uncompressed position, or for the uncompressed pad to compress to a particular height. Thus, if a downward force is applied to the pad to compress it and then the force is removed (the pad does not exert a downward force, but the elasticity of the pad causes an upward force to return to the uncompressed position). The time required for the pad to return from the compressed height to the decompressed height is defined as the pad relaxation time (TR).

The relaxation time (TR) of the pad can be determined by empirical means and will depend on the thickness of the pad, the material of the pad, and other properties of the pad. Pad relaxation time is Te
cQuipment SM106 Creep Machine or Nano Instrument
It can be determined using a device such as the Nano Indenter manufactured by.

The pad relaxation time (TR) above correlates to the periodic downward and upward forces on the wafer and pad. The periodic nature of the force is the time it takes a downward force on the pad (called THI), and the smaller force,
For example, the force may be substantially removed and the upward force due to the elasticity of the pad may be defined as the time it takes for the wafer (TLO). The sum of THI and TLO equals the cycle time of the periodic force and can be called TPM. THI
It is preferred that the forces be applied at equal periods so that TLO and TLO are equal. In such an equal period force process, the relaxation time (TR) of the pad is THI and TLO.
Greater than. Broadly speaking, the relaxation time of the pad (T
R) is longer than the time the pad is subjected to a downward force (compression) or an upward force (decompression).

Referring to FIG. 1, the different stages of pad compression and decompression can be described. The pad 13 is located on the platen 12 connected to the rotating shaft 14 in the figure. The following description also applies to linear transfer pads.
Pad 13 has a lower surface 13a located on the upper surface of platen 12 and an upper decompression surface 13c. 13c
At the pad decompression position, indicated by, the pad height can be defined as _HDC . Under compression, as indicated by the downward arrow, the pad is compressed to the height indicated by line 13b, which can be defined as H _C. The heights H _C and other heights defined above have a cyclic force
It is the same regardless of whether the pad is applied from above as shown in or from below.

In a typical chemical mechanical planarization process,
Pad 13 is compressed during steady state operation to a height indicated by line 13b, which compression is maintained during the chemical mechanical planarization process. In the process shown in U.S. Pat. No. 5,486,265, when the pressure is pulsed between an initial optimum pressure and a second reduced pressure, the pad is in the compressed position shown by line 13b and the decompressed position shown by line 13c. Change between

Applicants have determined that a chemical mechanical planarization process occurs when periodic downward and upward forces are exerted on the wafer or pad, and thus the pad, and the periodic force correlates with the relaxation time (TR) of the pad. Have been found to be significantly improved. That is, as shown in FIG. 1, during steady-state operation of the chemical mechanical planarization process, the method of the present invention provides that the pad height is between the compression height 13b and the decompression height 13c shown by the dotted lines 13d and 13e. Correlate such cyclic forces with the compressibility of the pad so that it is maintained in between. As shown in FIG. 1, the height of the pad between 13d and 13e is defined as H _op . It can be seen from the figure that the pad height is higher than the compression height 13b and lower than the decompression height 13c. Operating the chemical mechanical planarization process within the operating height range H _{op of} this pad significantly improves the process and enhances the planarization results.

With reference to FIGS. 2 and 3, the method and apparatus of the present invention can be demonstrated. FIG. 2 is a graph in which the force applied to the pad is measured with respect to the time the pressure is applied to the pad. Therefore, between times T ₀ and T ₁ (THI), the planarizing force on the pad is a high compressive force, indicated by P _HI ,
The pad is compressed. Between times T ₁ and T ₂ (TLO)
The force on the pad is a low force, P _Lo , and the pad is decompressed. The period between T ₀ and T ₂ can be defined as T _PM and represents one cycle of the periodic force on the pad. Although FIG. 2 is shown as a step function for clarity, it will be appreciated by those of ordinary skill in the art that this force is usually a sinusoidal curve that is gradually applied to the pad during pad compression and gradually removed during pad decompression. Can understand. However, for the purposes of this discussion, it is considered that the graphs shown in FIGS. 2 and 3 better describe the method and apparatus of the present invention.

FIG. 3 shows a graph of pad height versus time during a steady state planarization operation. The time shown in FIG. 3 is shown in FIG.
Corresponding to the inside time. Line A shows the height H during THI (and P _HI ) during the force cycle time T ₀ -T ₂ , which is the time interval that represents one cycle of downward and upward force on the pad.
It shows that we move from op1 to a lower height Hop2 and return to height Hop1 during TLO (and P _LO ). Pad heights Hop1 and Hop2 are in the uncompressed state (H
_It can be seen that it is within the pad height range under _DC ) and under compression (H _C ).

The planarization process according to line A is such that the relaxation time (TR) of the pad is less than the time the pad is under high pressure (P _HI ) or low pressure (P _LO ) as shown in FIG. Is also long, so it can operate.

The normal process, which uses pressure modulation but does not correlate the compressibility of the pad, can be represented by line B. Line B shows that when the relaxation time (TR) of the pad is shorter than the time the pad is under high or low pressure, the height of the pad during planarization is the decompression height (H _DC ) of the pad. And the compressed height (H _C ) of the pad.

Varying the time the pad is under high pressure (down force) or low pressure (up force) causes the pad to move between the compression and decompression positions, respectively, during steady state operation of this process. One of ordinary skill in the art will appreciate that height is affected. Assuming a uniform periodic force adjustment, where high or low force on the pad is equal in time,
Force period (TPM) is shortened or relaxation time (TPM)
Higher R) pads can be used, or both, to reduce pad height variations during the process. Therefore, Hop1 and Ho of line A in FIG.
p2 are closer to each other, resulting in a narrower pad height during operation. Similarly, if the cycle time for force adjustment changes at a constant pad relaxation time that is longer than the downward or upward force time, the shape of line A is also affected, and Hop1 increases as the cycle time increases. And Hop2 increase the pad height difference, and as the cycle time decreases, the pad height difference between Hop1 and Hop2 decreases.

Those skilled in the art will also understand that the adjustment of the periodic forces can be unequal so that the time at high force (THI) is longer or shorter than the time at low force (TLO). However, it will be appreciated that regardless of the cycle time, the relaxation time (TR) of the pad must still be longer than the time the pad is under compression or decompression. Thus, if the periodic distribution of forces is not equal, the time limit is the longer time that the pad is subjected to high or low forces. This time must be less than the pad relaxation time (TR).

In summary, the following matters will be disclosed regarding the configuration of the present invention.

(1) During planarization, applying periodic downward and upward forces to either the wafer or the pad pressed against the polishing pad, and the height of the pad in the prior art planarization process. Planarizing a workpiece in a chemical mechanical planarization process that includes correlating the periodic force with the compressibility of the pad to maintain it between a compression and decompression position as is commonly used. how to. (2) The method according to (1) above, wherein the chemical mechanical planarization process uses a rotating pad. (3) The method according to (1) above, wherein the chemical mechanical planarization process uses a linear transfer pad. (4) The method according to (1) above, wherein the workpiece is a semiconductor wafer. (5) Rotating turntable or linear movement platen,
Providing a chemical mechanical planarization device comprising a compressible planarization pad having a relaxation time TR on its surface;
Providing a planarizing slurry to the surface of the pad, providing a substrate to planarize, and periodically downwardly or to the substrate or the pad to maintain the substrate against the surface of the pad. Providing an upward force, the height of the pad being maintained between the decompression height and the compression height during the action of the force according to the equation: TR> TRI and TLO (where THI is the time when the pad is subjected to a downward force, TLO is the time when the pad is subjected to an upward force) and continuing the method until the substrate is planarized. Machine flattening method. (6) The method according to (5) above, wherein the flattening device uses a rotary turntable. (7) The planarization device uses a linear movement platen,
The method according to (5) above. (8) The method according to (5) above, wherein the substrate is a semiconductor wafer. (9) A rotary turntable or linear translation platen assembly, a compressible planarization pad supported on the assembly and having a relaxation time of TR, and fixed to the lower surface of the carrier, located above the assembly. And a rotatable carrier adapted to hold the workpiece positioned between the carrier and the planarizing pad during planarization, and a position for compressing the height of the pad during the planarizing process. And to maintain between the decompression position
An apparatus for planarizing a surface on a workpiece comprising the carrier and means for providing a periodic downward or upward force to the workpiece or to the pad. (10) The apparatus according to (9) above, wherein the assembly uses a rotatable turntable. (11) The apparatus according to (9) above, wherein the assembly uses a linear movement platen. (12) The apparatus according to (9) above, wherein the workpiece is a semiconductor wafer.

[Brief description of drawings]

FIG. 1 shows the different heights of pads during the planarization process according to the prior art and during the planarization process of the invention, CM
FIG. 6 is a schematic side view of a P-turn turntable and a planarizing pad assembly.

FIG. 2 is a graph showing the downward and upward force on the pad by the wafer and wafer carrier assembly versus time during the CMP process.

FIG. 3 is a graph showing changes in pad height versus time during a CMP process according to the prior art and during the CMP process of the present invention.

FIG. 4 is a schematic diagram of a typical prior art rotary CMP apparatus for planarizing a semiconductor wafer.

FIG. 5 is a schematic diagram of a typical prior art linear CMP apparatus for planarizing a semiconductor wafer.

[Explanation of symbols]

10 Flattening device 11 Planarizing wheel assembly 12 Platen 13 pads 14 shaft 16 wafers 17 Wafer Carrier Assembly 18 Wafer carrier 19 Pressure plate 20 spindles

Claims (3)

[Claims] 1. A method of applying periodic downward and upward forces to either a wafer or pad pressed against a polishing pad during planarization, the height of the pad being between a compression position and a decompression position. A method of planarizing a workpiece in a chemical mechanical planarization process comprising correlating the periodic force with the compressibility of the pad to maintain. 2. A chemical mechanical planarization apparatus comprising a rotary turntable or a linear movement platen and a compressible planarization pad having a relaxation time TR on its surface, and planarizing the surface of the pad. Providing a slurry, providing a planarizing substrate, and maintaining the substrate against the surface of the pad,
Providing a cyclic downward or upward force to the substrate or the pad such that the height of the pad is between the decompression height and the compression height during the action of the force according to the equation: TR> TRI and TLO (where THI is the time when the pad is subjected to a downward force, TLO is the time when the pad is subjected to an upward force) until the substrate is planarized. A step of continuing the method. 3. A rotary turntable or linear translation platen assembly, a compressible planarization pad supported on the assembly, and a carrier above the assembly and secured to a lower surface of the carrier. A rotatable carrier adapted to hold the workpiece between the planarization pad during planarization, and a height of the pad during compression and decompression positions during the planarization process. An apparatus for planarizing a surface on a workpiece comprising: a carrier and means for providing a periodic downward or upward force on the workpiece or on the pad for maintaining during maintenance.